The present invention relates generally to optical disk apparatuses, and more particularly to an optical disk apparatus which uses a 3.5 in optical disk and performs a so-called pull-in of a focus servo and a so-called pull-in of a tracking servo.
When a optical pickup of an optical disk apparatus seeks a target track, a focus servo and a tracking servo are first turned off and the optical pickup 52 is moved near the target track, along two shafts 51a and 51b, by a linear motor, as shown in FIG. 1. A conventional 5 in optical disk 50 comprises about 1000 read-in-tracks 53a at an inner part and about 1000 read-out-tracks 53b at an outer part. In addition, detectors 54 and 55, which respectively comprise dampers 54b and 55b and touch sensors 54a and 55a, are respectively provided near the read-in-tracks 53a and read-out-tracks 53b to prevent the optical pickup 52 from moving more inwardly than the read-in-tracks 53a or more outwardly than the read-out-tracks 53b. The respective touch sensors 54a and 55a detects a position of the optical pickup 52. The respective damper 54b and 55b prevent the optical pickup 52 from moving more inwardly than the read-in-tracks 53a or more outwardly than the read-out-tracks 53b.
Then the focus servo is turned on to perform a so-called pull-in of the focus servo and subsequently the tracking servo is turned on to perform a so-called pull-in of the tracking servo. Finally the optical pickup 52 starts to perform a seeking operation and is moved near the target track. Then the optical pickup 52 sequentially searches the target track by means of a track jump. Hereupon, the term "pull-in of the focus servo", as used herein, means a process for making an optical beam of the optical pickup focus on a recording surface of the optical disk. In addition, the term "pull-in of the tracking servo" as used herein, means an process for making an optical beam follow an arbitrary track. The pull-in of the focus servo can be achieved when the optical pickup is located at a reflection film area on the recording surface of the optical disk. On the other hand, the pull-in of the tracking servo can be achieved when the optical pickup is located at a track area on the recording surface of the optical disk. The track area, including the read-in-tracks to the read-out-tracks, is included in the reflection film area. Therefore, an area where both pull-in of the focus servo and pull-in of the tracking servo can be achieved is from and including the read-in-tracks to and including the read-out-tracks.
If the pull-in of the focus servo and the pull-in of the tracking servo cannot be properly achieved, the optical pickup cannot read an address number recorded in each track and thus will be at a loss to recognize where it is. As a result, it cannot seek the target track. Therefore, stable pull-in of the focus servo and the pull-in of the tracking servo achieves a stable and quick access operation. Generally, the pull-in of the focus servo and the pull-in of the tracking servo are performed when the optical disk storage is started or reset from a power-saving mode Incidentally, "a power-saving mode" is described in detail in U.S. patent application Ser. No. 731,500 previously filed by this applicant.
However, in an optical disk storage using a 3.5 inch optical disk, it is desirable to omit the detectors 54 and 55 shown in FIG. 1 from the standpoint of miniaturization, cost reduction and simplicity. However, such an optical disk storage in which the detectors 54 and 55 are omitted has not been developed in which the pull-in of the focus servo and the pull-in of the tracking servo can be achieved. In addition, since a 3.5 in optical disk has a few read-in-tracks, it is difficult for the optical pickup to detect them and stop there. Likewise, a 3.5 in optical disk has only about 300 read-out-tracks. Therefore, the following problems occur at the inner part and the outer part of the optical disk:
1. If the optical pickup is located at the non-reflection film area, the pull-in of the focus servo cannot achieved. PA1 2. Even if the pull-in of the focus servo can be achieved, if the optical pickup is located at the non-track area, the pull-in of the tracking servo cannot achieved.